What is the most common type of spyware?

Adware is a type of software that is used to track a user's online activity and display ads.  https://sakeradvantage.com/?p=1724 Other common types of spyware include keyloggers, which are used to track a user's keystrokes, and Trojans, which are used to take individual information. https://tourismcrisis.org/?p=336